In this study, effects of naphthalene (NAP) exposure on plasma levels of 17-β estradiol and concentrations of neurotransmitters in different brain regions of female Klunzinger's mullet, at the previtellogenic and vitellogenic stages were examined. Studied neurotransmitters were noradrenalin (NA), serotonin (5-HT), dopamine (DA), and 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxy-3-indoleacetic acid (5HIAA). In the short- term stress experiment, fish were i.p. injected with 2 μl/g vegetable oil alone (control) or oil containing NAP (50 mg/kg body weight).
To study the long-term effect of NAP an amount of (50 mg/kg NAP +10 μl/g coconut oil) as i.p. implant and 10 μl/g coconut oil alone for control group. After long-term exposure, 17-β estradiol level in the plasma decreased in both stages fish. Monoamines analyses showed changes induced by NAP which depended upon the type of neurotransmitter and exhibited a marked brain regional selectivity. According to the results, NAP had more disturbing effects at the previtellogenic than the vitellogenic stages. Serotonergic system responded to the NAP exposure rapidly whereas dopaminergic system changed during the chronic naphthalene stress. The mentioned disturbing effects of naphthalene
on the brain monoaminergic systems may cause some endocrine disruptions especially in the hypothalamus-pituitarygonad axis and finally affect the vitellogenesis process and final oocyte maturation. Reduction in the plasma levels of 17-β estradiol during the naphthalene exposure probably are related biological feedbacks of neurotransmitters on the pituitary.